Abstract. The measurement of science achievement is often unnecessarily restricted to the presentation of reading comprehension items that are sometimes enriched with graphs, tables, and figures. In a newly developed viewing comprehension task, participants watched short videos covering different science topics and were subsequently asked several multiple-choice comprehension questions. Research questions were whether viewing comprehension (1) can be measured adequately, (2) is perfectly collinear with reading comprehension, and (3) can be regarded as a linear function of reasoning and acquired knowledge. High-school students (N = 216) worked on a paperbased reading comprehension task, a viewing comprehension task delivered on handheld devices, a sciences knowledge test, and three fluid intelligence measures. The data show that, first, the new viewing comprehension test worked psychometrically fine; second, performance in both comprehension tasks was essentially perfectly collinear; third, fluid intelligence and domain-specific knowledge fully accounted for the ability to comprehend texts and videos. We conclude that neither test medium (paper-pencil versus handheld device) nor test modality (reading versus viewing) are decisive for comprehension ability in the natural sciences. Fluid intelligence and, even more strongly, domain-specific knowledge turned out to be exhaustive predictors of comprehension performance.